Letters: May/June 2010

Home Energy Yardstick

In the January/February 2010 article “Energy Labeling and Energy Billing Analysis”, the authors note, “more than one-third of all homes will have energy use attributes that differ by more than 40% from the Yardstick projection.” This is a mischaracterization of the tool, because the Home Energy Yardstick does not predict future energy use like a simulation. The Yardstick score is based on the ratio of the homeowner’s actual energy consumption to the mean energy consumption of homes in the 2005 RECS with similar size, CDD, HDD, and number of occupants. It is a comparison of actual energy use to the mean energy use of homes with similar energy dependent characteristics. It was designed as a screening tool for benchmarking single-family homes, allowing homeowners to gauge their relative energy consumption and impact on the environment.

The Yardstick has several unique benefits that differentiate it from the HERS Index, as shown in the HERS Index versus Yardstick chart. One major advantage is the low cost and ease of use. The Yardstick requires only the homeowner’s time to gather 12 consecutive months of consumption data from their utility, knowledge of the home’s square footage, the number of people living in the home, and the ZIP code. It can also serve as an inexpensive screening tool for energy efficiency programs to target homes that score poorly for follow-up audits, home energy ratings, or whole house assessments. The Home Energy Yardstick can be found at www.energystar.gov/yardstick. For more detailed information on how the Yardstick works, please contact me at Leopkey.ted@epa.gov.

Ted Leopkey
Program Analyst
U.S. EPA

Authors Philip Fairey and David Goldstein reply:

The authors appreciate the usefulness of EPA's “Yardstick” and intended to make its usefulness clear in the article. Mr. Leopkey appears to have missed our point somewhat when he says that we mischaracterized this tool. He chose to quote a specific phrase from the article without consideration of the following sentence, which reads, “Thus, the physical attributes of any given home can be severely over or under estimated by the Yardstick.” Please note that this sentence is referring to the physical attributes of the home rather than its actual energy use at any particular time.

This is, in fact, the point that we were attempting to impart: that while the measured energy use of a home may well characterize the energy use of specific occupants of that home, it is likely not to characterize the energy use of some other set of occupants of that home. This is due to the fact that so much of a home's energy use is a direct result of the lifestyle influences of the particular occupant.

Our paper distinguishes between asset ratings that measure efficiency and operational ratings that measure bills and thus include both behavior and efficiency without distinguishing between the two. One might also look at the ratio of the two to tease out behavioral effects.

The HERS index rates efficiency and projects what bills would be if the occupant manages the home in a “standard” fashion. The Yardstick looks at comparative use without regard to efficiency. Since efficiency is related to bills on average, but with lots of variation based on behavior, either index will tell us something about what it isn’t measuring directly but will have lots of uncertainty.

As a result, it is the authors’ contention that the only way to assess equitably the physical attributes of one home as it might be compared with another home in the marketplace is to use a standardized set of operating conditions rather than the specific lifestyle influences of any particular set of occupants.

Lots to Learn about HVAC

I am a fellow HERS rater based in Southern Cal. I have enjoyed many an article from Steve Mann in Home Energy magazine. First of all, thank you, Steve, for your contributions. They address many issues that we as energy professionals encounter in our daily life.

I want to comment on your piece about NCI and the experience you had in their classes (“Comfort to the Maxx,” Jan/Feb ’10). First, some street cred: I’ve been a part of the HVAC industry since 1973. Starting as a parts guy, I have been an installer, service tech, construction and service manager, outside sales, estimating and design, and had my own small HVAC company as well. I have had the opportunity to teach it at our local community college and for Sempra and CHEERS. Having said that, I must add that I have much to learn, and indeed do that very thing daily.

I have taken classes and have been subsequently certified by NCI for air balancing through the NBI (National Balancing Institute) program. Over the years, I have returned from time to time for recertification. I have to agree with your comments about your experience. It appears to me that NCI is as much a marketing as a technical training organization. I have had similar experiences in that the instructor tends to spend time on third-party stories and rushing through—or skipping—material that was supposed to be covered. Additionally, I agree with your assertion that the exam questions tend to be spoon fed. In fairness, however, there are some other organizations that have similar standards when it comes to passing a “certification” exam.

On the other hand, the information presented by NCI has helped me countless times on residential and commercial air balance jobs; it has paid for itself many times over, believe me.

I applaud your efforts to learn more about a daunting subject. HVAC is our largest energy hog.

I look forward to meeting you at the CABEC conference in May. The preliminary agenda she sent out looks to be very interesting. Meanwhile, please keep those great articles coming!

Thanks very much for your comments. It's especially gratifying that a seasoned HVAC professional like yourself generally agrees with my assessment of the NCI courses. And you're right; there are many organizations that have similar certification standards (the two exceptions I have found are the LEED exams and the BPI exams). It's unfortunate but true. Not working with HVAC every day, I don't really get a chance to use the information that NCI gave me on a daily basis. However, I wish I did. I think it's probably a great framework to take into the field every day.

On another note—I'm glad you are coming to the CABEC conference. I think energy consultants, HERS raters, building science professionals, and HVAC professionals need to hang out together more. We could learn a lot from each other. See you there.

No Regrets

Great article (“Comfort to the Maxx,” Jan/Feb ’10)! I am a home performance auditor with a good understanding of HVAC with moderate field experience. I think Steve Mann nailed the experience I had while taking the course he described. I had to beat my head against a few walls after the course to truly begin to understand the information presented. It has been an excellent base, however, to provide clients with a perspective that is severely lacking in our area. I have regretted a number of training experiences, as many cannot be applied. This was not one of them.
Thanks for sharing a positive experience to move folks in the right direction.

Eric Elliott
Build With Vision
Boise, Idaho

Steve Mann replies:

I agree with you about the head banging, the severely lacking perspective, and the regrettable training experiences. It sounds like, based on your comments, I communicated that pretty well—always good to hear for a writer. Thanks very much for the feedback.

Up on Elevators

Typical traction elevator machine. (Image credit: Henry Gifford)

I have a reputation among students and colleagues as being honest, demanding, fair, and rigorous in grading (and in the awarding of praise). I was surprised and delighted to encounter an article about elevator energy use by Henry Gifford in the Jan/Feb ’10 issue of Home Energy (“Elevator Energy Use”). The article was well written, the topic was novel, and the content was at an appropriate technical level, data supported, relevant, practical, and interesting. I have enjoyed reading and learning from Henry’s many articles and Web postings, which have covered an impressive range of topics related to building energy conservation. The elevator article is the latest case in point. Thanks.

I want to also express my appreciation and support to Home Energy staff members for their willingness to encourage and publish articles on novel topics related to energy conservation in buildings.

Allen Zimmerman
Ohio State University, Wooster Campus
Wooster, Ohio

Wooster, Ohio Software Search

I've just read Steve Mann’s article entitled Energy Modeling Versus Reality (Jan/Feb ’10). Steve’s comments mirror much of what I hear from home energy auditors. We are a design/build firm specializing in green modular homes and are looking for the best analytical software to serve our design optimization needs. I am specifically looking at REM:Design, as we would optimally like to design to reduce our HERS as much as possible. I'm wondering if you could offer me some insight and perhaps a specific recommendation of software that will mitigate the majority of issues you discuss in your article. I greatly appreciate any response on this and look forward to your articles in the future.

Jeremy Davis
New World Home LLC
New York, New York

Author Steve Mann replies:

I'm glad you enjoyed the article. If you are looking at HERS ratings, you have only two choices—REM:Rate and EnergyGauge. Neither of them does a great job in my estimation, at least as far as utility bill disaggregation goes (which is what my article was all about). They both do a pretty good job on HERS rating, retrofit alternatives analysis, and reporting. Treat claims to do good utility bill disaggregation, but it isn’t RESNET approved for HERS ratings. I've had a few readers tell me WrightSoft is excellent for doing load calcs and utility bill disaggregation, but it doesn’t do HERS ratings either.

If you're just looking at design optimization, and not RESNET-approved HERS ratings, there are lots of other choices out there. (Note, there may be a big difference between a low HERS score and a truly energy-efficient building.) We use EnergyPro in California, which calculates ASHRAE loads, which can be used as a measure of optimization. There are also a bunch of programs listed on the DOE Web site at http://apps1.eere.energy.gov/buildings/tools_directory/alpha_list.cfm.

Finally, if you Google Energy Modeling Software, the first page of hits has some interesting information as well.

I thought my article was pretty clear in describing the problem, and pointing out that there is no good solution as far as I can tell (which is what you're asking). Maybe it wasn't as clear as I thought? If I find something I think is really good, believe me, I'll write about it as soon as I can try it out.

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